This invention relates to a process for extracting bitumen from oil sand. Oil sand is found in many parts of the world, in particular in Canada, the U.S.A., Venezuela, the U.S.S.R. and Malagasy.
Bitumen is presently commercially extracted in Canada from mined oil sand using a Hot Water Process. In accordance with this process, the oil sand is first mixed with water, caustic soda and steam in a rotating horizontal tumbler, called a conditioning drum. In this operation the components of the oil sand (i.e. bitumen, water and solids) are dispersed by a combination of heating and dilution with water. More particularly, the oil sand comprises grains having oil trapped therebetween. As water is added the sand grains collect therein; the bitumen separates from the grains and forms discrete flecks.
The slurry formed in the conditioning drum is then diluted with additional water and introduced into a separation vessel. This vessel has a cylindrical body and a conical bottom. Here the coarse sand grains drop the bottom of the vessel and are removed through an outlet as a tailings stream. This stream is discarded into a pond system. The bitumen flecks, which are slightly less dense than water because of the high process temperature, attach themselves to gas bubbles entrained in the slurry, rise through the vessel contents and form a froth product. This product over-flows the vessel wall into a launder and is collected. The fine solids remain largely suspended in the water of the separation vessel.
There are several problems of interest in the existing process. Firstly, there are difficulties connected with the bitumen flotation operation going on in the separation vessel. More particularly, if a large concentration of solids is present in the contents of the separation vessel, these solids will impede the upward progress of the aerated bitumen. Therefore, in order for the aerated bitumen to rise quickly through the vessel contents, it is desirable to have a dilute system within the vessel. This means that a relatively large amount of water must therefore be used in the process. Since this water must be heated to about 190.degree. F., the energy requirement of the process are therefore increased as the water content is increased. Because large amounts of water are introduced into the process, it is necessary to withdraw a middlings dragstream from the midpoint of the vessel to maintain a balance. This middlings dragstream is treated in a subaerated flotation cell to recover contained bitumen, and is then discarded into the pond system. Unfortunately, fine solids (-325 Mesh), particularly clay, associated with the oil sand, pass through the process and end up suspended in the tailings water of the pond system. The presence of caustic soda in the tailings water influences these clay particles so that they settle extremely slowly and therefore the water must be held for a prolonged period in the pond before it is low enough in solids to be reused in the process. This then requires that inordinarily large tailings ponds be provided. In summary, the flotation mechanism in the prior art requires that large amounts of heated water be used and that solids removal in the ponds be extensive, thereby necessitating an extensive pond system.
In U.S. patent application Ser. No. 913,593 filed June 8, 1978 and now abandonded a process is claimed wherein an aqueous slurry of oil sand is brought into contact with an immersed, apertured, oleophilic surface in a water bath. The oil from the sand adheres to the immersed, oleophilic surface and the sand particles pass through the apertures. The oleophilic surface is then moved out of the water and the oil is removed from the oleophilic surface out of the water bath. While this process efficiently separates oil from an oil sand it requires both below and above water operations and considerably limits the size of the separation equipment which can be used and recovery of the oil from the oleophilic surface.